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A nautical mile (nmi) is a unit of measurement used for sea and air travel, equal to 6,076 feet or 1,852 meters.
Quick Facts:
A nautical mile is based directly on the size and shape of the Earth.
It is defined as one minute of arc along a meridian (a line of longitude).
Imagine the Earth as a circle of 360 degrees. Each of those degrees is divided into 60 smaller parts called "minutes."
One nautical mile is equal to one of these minutes of latitude.
This direct link to the planet's geometry makes the nautical mile essential for navigators, as it simplifies calculations on maps and charts.
While they both measure distance, nautical miles and statute miles (used on land) are not the same.
The key difference lies in how they are calculated and used.
Statute Mile: This is the mile you know from road signs, equal to 5,280 feet. It's a fixed distance that doesn't take into account the Earth's curvature.
Nautical Mile: This is a longer measurement, approximately 1.15 statute miles (6,076 feet). It is based on the Earth's curvature, aligning with the degrees of latitude and longitude used on navigational charts.
Using statute miles for long-distance sea or air travel would lead to significant errors, which is why navigators exclusively use nautical miles to ensure accuracy.
In maritime and aviation, speed isn't measured in miles per hour—it's measured in knots.
A knot is a unit of speed, not distance.
It is defined simply as one nautical mile per hour. This makes calculations very straightforward: a ship traveling at a steady 15 knots will cover 15 nautical miles in precisely one hour.
The term comes from the old sailors' practice of using a rope with knots tied at regular intervals, thrown overboard, to measure a ship's speed.